Pluripotent stem cells (PSCs), including human PSCs (hPSCs) and induced PSCs (iPSCs) are being examined as potential sources of cells for the treatment of a wide variety of diseases. Stem cells and cells differentiated or partially differentiated from such stem cells are also being explored for use in ex vivo tissue engineering and in vitro drug screening and toxicology studies.
The use of stem cells in commercial and clinical applications will require large-scale growth techniques that do not induce differentiation of the cell cultures (i.e. maintaining the stem cells under conditions of self-renewal).
Reliable methods for maintaining and expanding stem cells are of broad interest. In fact, for the success of potential clinical and industrial stem cell applications, it is absolutely essential to find conditions that allow production of large amounts of stem cells under defined conditions and at reasonable cost. This is not a trivial problem and satisfactory solutions are actively sought.
The commonly used feeder-free substrate for human pluripotent stem cells is Matrigel (BD), which is a poorly defined extracellular matrix (ECM) derived from mouse sarcomas. Therefore, there is a great interest in developing defined synthetic substrates to act as support for pluripotent and multipotent cells. Several synthetic substrates have been developed, and most contain recombinant peptides [1-10]. Such peptide-based substrates are expensive, which may make their use in large-scale expansion of stem cells cost-prohibitive.
In contrast, some less expensive substrates have been developed using synthetic chemical components and polymers. These synthetic substrates provide platforms that may be useful for industrial applications that require large numbers of stem cells in an undifferentiated or partially differentiated state. These synthetic substrates are based on aminopropylmethacrylamide (APMAAm) [11], poly[2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl) ammonium hydroxide] (PMEDSAH [12, 13], and poly(methyl vinyl ether-alt-maleic anhydride) (PMVE-alt-MA) [14].
All three synthetic substrates (APMAAm, PMEDSAH and PMVE-alt-MA) were used with bovine serum albumin (BSA)-containing defined medium. In the case of APMAAm, it has been shown that BSA was critical for cell attachment. Attachment and proliferation of hESCs on this substrate was compromised as compared to Matrigel [11]. In the case of PMEDSAH, good results were only obtained with one of the 2 human embryonic stem cell (hESC) lines tested when defined media were used, and good results with the one cell line were only achieved with StemPro medium, but not with mTeSR1 medium[13].
Chen et al. (Nat. Methods 8(5), 424-429 (2011)) describes a completely defined albumin-free medium (E 8) containing 8 essential components. In the conditions described by Chen et al., the defined medium is used in conjunction with surfaces coated with recombinant vitronectin (vitronectin-N).
Polydopamine-coated polystyrene and poly-lactic-co-glycolic acid has been used for the proliferation and differentiation of human neural stem cells (Yang et al., Biomaterials 33(29), 6952-64).
The use of stem cells in industrial applications depends on the ability to design culture conditions that are chemically defined, robust, cost-effective and which may be devoid of animal-derived components, if desired.